[Misc] Load FP8 kv-cache scaling factors from checkpoints (#4893)

The 2nd PR for #4532.

This PR supports loading FP8 kv-cache scaling factors from a FP8 checkpoint (with .kv_scale parameter).

vllm/model_executor/models/gpt_bigcode.py

@@ -88,7 +88,8 @@ class GPTBigCodeAttention(nn.Module):
                               self.head_dim,
                               scale=self.scale,
                               num_kv_heads=self.num_kv_heads,
-                              cache_config=cache_config)
+                              cache_config=cache_config,
+                              quant_config=quant_config)
 
     def forward(
         self,